1. Field of the Invention
The present invention relates to magnetic sensing elements of a current-perpendicular-to-the-plane (CPP) type. More particularly, the invention relates to a magnetic sensing element in which the rate of change in resistance can be improved and a high read-sensitivity and a high output can be obtained, and to a thin-film magnetic head including the magnetic sensing element.
2. Description of the Related Art
FIG. 14 is a partial sectional view which shows the structure of a conventional magnetic sensing element, viewed from the surface facing a recording medium.
In the magnetic sensing element shown in FIG. 14, an antiferromagnetic layer (lower antiferromagnetic layer) 4 composed of a PtMn alloy or the like is formed on an underlayer 6 composed of Ta or the like. A pinned magnetic layer (lower pinned magnetic layer) 3 composed of an NiFe alloy or the like is formed on the antiferromagnetic layer 4, and a nonmagnetic interlayer (lower nonmagnetic interlayer) 2 composed of Cu or the like is formed on the pinned magnetic layer 3. A free magnetic layer 1 composed of an NiFe alloy or the like is formed on the nonmagnetic interlayer 2.
Another nonmagnetic interlayer (upper nonmagnetic interlayer) 2, another pinned magnetic layer (upper pinned magnetic layer) 3, and another antiferromagnetic layer (upper antiferromagnetic layer) 4 are deposited on the free magnetic layer 1 in that order. A protective layer 7 composed of Ta or the like is formed on the upper antiferromagnetic layer 4.
The layers from the underlayer 6 to the protective layer 7 together constitute a multilayer film 10. Hard bias layers 5 are formed on both sides in the track width direction (in the X direction in the drawing) of the multilayer film 10, and electrode layers 11 are formed on the hard bias layers 5.
This magnetic sensing element is a so-called xe2x80x9cdual spin-valve thin-film elementxe2x80x9d in which the pinned magnetic layer 3 and the antiferromagnetic layer 4 are disposed on each surface of the free magnetic layer 1 with the nonmagnetic interlayer 2 therebetween.
In the magnetic sensing element shown in FIG. 14, the magnetization direction of the pinned magnetic layer 3 is pinned in the height direction (in the Y direction in the drawing) by an exchange coupling magnetic field generated between the pinned magnetic layer 3 and the antiferromagnetic layer 4. The magnetization direction of the free magnetic layer 1 is aligned in the track width direction (in the X direction) by a longitudinal bias magnetic field from the hard bias layer 5.
In the dual spin-valve thin-film element shown in FIG. 14, since the number of interfaces at which electron scattering occurs is twice as many as a single spin-valve thin-film element which includes an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic interlayer, and free magnetic layer, each one layer, an improvement in the rate of change in resistance is expected.
In the magnetic sensing element shown in FIG. 14, a sensing current flows substantially parallel to the planes of the individual layers of the multilayer film 10, that is, the element is referred to as a xe2x80x9ccurrent-in-the-plane (CIP)xe2x80x9d type element.
On the other hand, an element in which a sensing current flows perpendicular to the individual layers of the multilayer film 10 is referred to as a xe2x80x9ccurrent-perpendicular-to-the-plane (CPP)xe2x80x9d type element.
When the element is miniaturized as the recording density is increased, and in particular, when the area of an element in the direction parallel to the planes of the individual layers is decreased to 0.1 xcexcm square or less, it is known that the read output can be increased by selecting the CPP type instead of the CIP type.
Therefore, in order to improve both the read output and the rate of change in resistance as the recording density is further increased in future, a magnetic sensing element of a CPP type having a dual structure is thought to be desirable.
FIG. 15 is a schematic diagram showing a structure of a CPP-type dual spin-valve thin-film element.
The giant magnetoresistance (GMR) effect in a magnetic sensing element is mainly caused by xe2x80x9cspin-dependent scatteringxe2x80x9d of electrons. That is, the GMR effect is obtained by using the difference between the mean free path xcex+ of the conduction electrons (e.g., spin-up electrons) having a spin parallel to the magnetization direction of a magnetic material, i.e., herein, a free magnetic layer, and the mean free path xcexxe2x88x92 of the conduction electrons (e.g., spin-down electrons) having a spin antiparallel to the magnetization direction of the free magnetic layer.
In the CPP-type magnetic sensing element, since the current flows perpendicular to the planes of the individual layers, the length of the current path of the sensing current flowing through a free magnetic layer, a nonmagnetic interlayer, and a pinned magnetic layer, which participate in the magnetoresistance effect, is shorter compared to the CIP-type magnetic sensing element in which the sensing current flows substantially parallel to the planes of the individual layers.
Therefore, if the thickness of the pinned magnetic layer and the thickness of the free magnetic layer are small, the conduction electrons, for example, spin-down electrons, which are not supposed to pass through the magnetic layers in the CIP type, pass through the magnetic layers together with the spin-up conduction electrons in the CPP type. It is not possible to increase the difference between the mean free path xcex+ of the spin-up conduction electrons and the mean free path xcexxe2x88x92 of the spin-down conduction electrons, and the rate of change in resistance cannot be improved.
Although an attempt has been made to improve the rate of change in resistance by increasing the thickness of the pinned magnetic layer and the thickness of the free magnetic layer so that the bulk scattering effect is satisfactorily displayed, if the thickness of the free magnetic layer is increased, variations in the magnetization of the free magnetic layer in response to an external magnetic field become dull because of an increase in the magnetic moment.
The magnetic moment of the free magnetic layer is determined by the product of the saturation magnetization Ms and the thickness t1. The magnetic moment is an index of variability of the magnetization of the magnetic layer in response to an external magnetic field. That is, if the magnetic moment is increased, variability of the magnetization of the magnetic layer having the magnetic moment in response to the external magnetic field is weakened.
In the magnetic sensing element, the magnetization of the pinned magnetic layer is pinned in a predetermined direction and the magnetization of the free magnetic layer varies in response to an external magnetic field, resulting in a change in the electrical resistance, and thereby external signals are detected. Therefore, the magnetization of the free magnetic layer must vary with the external magnetic field sensitively. In the CPP type, however, if the thickness of the free magnetic layer is increased to display the bulk scattering effect, the magnetic moment of the free magnetic layer is increased, and as a result, the sensitivity to the external magnetic field is decreased and it is not possible to improve the read output appropriately.
As described above, in the conventional CPP-type magnetic sensing element, it is not possible to improve both the read output and the rate of change in resistance simultaneously.
With respect to the CPP-type dual spin-valve thin-film element, since the number of layers can be increased and the number of the interfaces at which electron scattering occurs is increased compared to the single spin-valve thin-film element, an improvement in the rate of change in resistance is expected. However, a further improvement in the rate of change in resistance is desired to meet the demands for higher recording densities.
It is an object of the present invention to provide a CPP-type magnetic sensing element in which the rate of change in resistance can be improved and an excellent read-sensitivity and a high output can be obtained.
It is another object of the present invention to provide a thin-film magnetic head in which the gap of the MR head can be narrowed even if the total thickness of the magnetic sensing element is increased and which is suitable for a future increase in the recording densities.
In one aspect of the present invention, a magnetic sensing element includes a multilayer film including a free magnetic layer, an upper nonmagnetic interlayer placed on the free magnetic layer, a lower nonmagnetic interlayer placed under the free magnetic layer, an upper pinned magnetic layer placed on the upper nonmagnetic interlayer, a lower pinned magnetic layer placed under the lower nonmagnetic interlayer, an upper antiferromagnetic layer placed on the upper pinned magnetic layer, the upper antiferromagnetic layer pinning the magnetization direction of the upper pinned magnetic layer in a predetermined direction by an exchange coupling magnetic field, and a lower antiferromagnetic layer placed under the lower pinned magnetic layer, the lower antiferromagnetic layer pinning the magnetization direction of the lower pinned magnetic layer in a predetermined direction by an exchange coupling magnetic field, wherein a current flows perpendicular to the planes of the individual layers of the multilayer film, and the free magnetic layer includes at least two magnetic sublayers and an intermediate sublayer placed between the two adjacent magnetic sublayers.
The magnetic sensing element of the present invention is a CPP-type dual spin-valve thin-film element in which a sensing current flows perpendicular to the planes of the individual layers of the multilayer film.
In the present invention, in order to increase the physical thickness and to decrease the resultant magnetic moment of the free magnetic layer by decreasing the magnetic thickness, the free magnetic layer is formed to as to include at least two magnetic sublayers and the intermediate sublayer placed between the two adjacent magnetic sublayers. That is, the individual magnetic sublayers constituting the free magnetic layer are magnetized antiparallel to the magnetization direction of the opposed magnetic sublayers, and thus the free magnetic layer has a ferrimagnetic structure.
In the CPP-type magnetic sensing element having such a structure, by increasing the thicknesses of the magnetic sublayers, it is possible to display the bulk scattering effect satisfactorily, resulting in an improvement in the rate of change in resistance, and it is also possible to decrease the resultant magnetic moment which is the vector sum of the magnetic moments of all the magnetic sublayers. Consequently, the magnetization of the free magnetic layer varies satisfactorily in response to an external magnetic field, and it is possible to improve the read output.
As will be described in detail with reference to the drawings, with respect to a CPP-type dual spin-valve thin-film element having a free magnetic layer with the ferrimagnetic structure as is the case of the present invention, an equivalent circuit representing spots which display the magnetoresistance effect due to a change in electrical resistance is a series circuit.
On the other hand, with respect to a CIP-type dual spin-valve thin-film element having a free magnetic layer with the ferrimagnetic structure, an equivalent circuit representing spots which display the magnetoresistance effect due to a change in electrical resistance is a parallel circuit.
Therefore, it is possible to manufacture a magnetic sensing element having a higher rate of change in resistance effectively by using the CPP-type dual spin-valve thin-film element compared to the CIP-type dual spin-valve thin-film element.
In another aspect of the present invention, a magnetic sensing element includes at least two multilayer films, each including a free magnetic layer, an upper nonmagnetic interlayer placed on the free magnetic layer, a lower nonmagnetic interlayer placed under the free magnetic layer, an upper pinned magnetic layer placed on the upper nonmagnetic interlayer, and a lower pinned magnetic layer placed under the lower nonmagnetic interlayer; an intermediate antiferromagnetic layer placed between the two adjacent multilayer films; a lower antiferromagnetic layer placed under the lower surface of the multilayer film located at the bottom of the element; and an upper antiferromagnetic layer placed on the upper surface of the multilayer film located on the top of the element, wherein the magnetization direction of each of the upper pinned magnetic layer and the lower pinned magnetic layer is pinned in a predetermined direction by an exchange coupling magnetic field generated between the pinned magnetic layer and any one of the antiferromagnetic layers, and a current flows perpendicular to the planes of the individual layers.
In the magnetic sensing element of the present invention having the configuration described above, at least two free magnetic layers are provided. In the dual spin-valve thin-film element described above, one free magnetic layer is provided. By providing at least two free magnetic layers, the number of interfaces at which electron scattering occurs can be further increased, and it is possible to manufacture a magnetic sensing element in which the rate of change in resistance can be more effectively improved compared to the configuration of the dual spin-valve thin-film element.
Preferably, the free magnetic layer includes at least two magnetic sublayers and an intermediate sublayer placed between the two adjacent magnetic sublayers. Consequently, the free magnetic layer can have a ferrimagnetic structure. Since the physical thickness of the free magnetic layer can be increased and the magnetic thickness can be decreased, the rate of change in resistance can be further improved and the read output can be further improved.
In the present invention, preferably, the thickness of the magnetic sublayer adjoining the nonmagnetic interlayer is in the range of 40 xc3x85 to 100 xc3x85. Consequently, the bulk scattering effect can be satisfactorily displayed and the rate of change in resistance can be further improved.
In the present invention, when the number of magnetic sublayers is two, the total thickness of the magnetic sublayers is preferably in the range of 85 xc3x85 to 195 xc3x85. Consequently, the physical thickness of the free magnetic layer can be increased, and the rate of change in resistance can be further improved.
In the present invention, when the number of magnetic sublayers is two, the resultant magnetic moment (saturation magnetization Msxc3x97thickness t) of the free magnetic layer is preferably in the range of 5 Txc2x7xc3x85 to 60 Txc2x7xc3x85. Consequently, the magnetic thickness of the free magnetic layer can be decreased, and it is possible to obtain a magnetic sensing element in which the magnetization varies sensitively in response to an external magnetic field and the read output is increased.
More preferably, the resultant magnetic moment is 30 Txc2x7xc3x85 or less.
In the present invention, preferably, three magnetic sublayers constitute the free magnetic layer, and the magnetic sublayer in contact with the upper nonmagnetic interlayer and the magnetic sublayer in contact with the lower nonmagnetic interlayer are magnetized in the same direction. In such a magnetization state, manufacturing of the magnetic sensing element is facilitated.
In such a case, the total thickness of the magnetic sublayers is preferably 85 xc3x85 to 295 xc3x85, and the resultant magnetic moment (saturation magnetization Msxc3x97thickness t) of the free magnetic layer is preferably 45 Txc2x7xc3x85 to 195 Txc2x7xc3x85. Consequently, the physical thickness of the free magnetic layer can be increased, and the rate of change in resistance can be further increased. The magnetic thickness of the free magnetic layer can be decreased, and it is possible to obtain a magnetic sensing element in which the magnetization varies sensitively in response to an external magnetic field and the read output is increased.
In the present invention, preferably, the pinned magnetic layer includes two magnetic sublayers and an intermediate sublayer placed between the magnetic sublayers. Thus, the pinned magnetic layer has a so-called ferrimagnetic structure. Consequently, the physical thickness of the pinned magnetic layer can be increased, and the apparent magnitude of an exchange coupling magnetic field generated between the pinned magnetic layer and the antiferromagnetic layer can be increased. As a result, the rate of change in resistance can be improved and the magnetization of the pinned magnetic layer can be appropriately pinned.
In the present invention, preferably, the magnetic sensing element recedes from a surface facing a recording medium in the height direction, a flux guide layer extends from the front end of the free magnetic layer to the surface facing the recording medium, the flux guide layer being integrally formed with the free magnetic layer or being magnetically coupled to the free magnetic layer, and the flux guide layer is exposed at the surface facing the recording medium.
Preferably, the width in the track width direction of the flux guide layer at the surface facing the recording medium is smaller than the width in the track width direction of the free magnetic layer.
In another aspect of the present invention, a thin-film magnetic head of the present invention includes the magnetic sensing element described above, and upper and lower shielding layers provided on and under the flux guide layer with gap layers therebetween.
As described above, in the thin-film magnetic head of the present invention, the magnetic sensing element recedes in the height direction from the surface facing the recording medium, and the front end of the flux guide layer is exposed at the surface facing the recording medium. When an external magnetic field is introduced from the flux guide layer, the magnetization direction of the free magnetic layer magnetically coupled to the flux guide layer is varied, thus displaying the GMR effect.
In the present invention, since the shielding layers are provided on and under the flux guide layer with the gap layers therebetween, the gap can be narrowed appropriately, and it is possible to manufacture a thin-film magnetic head which is suitable for the future increase in the recording densities.
The thin-film magnetic head of the present invention, preferably includes a back yoke layer provided on the surface opposite to the surface facing the recording medium, the back yoke layer being integrally formed with the free magnetic layer or being magnetically coupled to the free magnetic layer, and a base of the shielding layer located above the flux guide layer may be magnetically coupled to the back yoke layer.
In such a configuration, an inductive head for writing can be formed using the flux guide layer, the free magnetic layer, the back yoke layer, and the upper shielding layer.
That is, in the present invention, gap narrowing can be achieved, and the MR head for reading and the inductive head for writing can be formed with a small number of layers, thus facilitating the manufacturing process.